Such an apparatus is useful in several technical fields, for example, when separating fine catalyst particles which are in suspension in a hydrocarbon feedstock, which feedstock comes from a catalytic cracking unit.
From French patent No. 2,587,629 (which corresponds to U.S. application Ser. No. 639,756, now U.S. Pat. No. 5,074,989, incorporated herein by reference), a separating apparatus of this type is known which comprises a bundle of cylindrical tubes or barrier tubes made of a mineral substance, for example, alumina or carbon, which are internally coated with one or more coats of metallic oxides. These tubes are mounted in parallel in a metallic unit known as a module, which module comprises a cylindrical shell that is closed at its ends by end walls. The latter are perforated with orifices into which the ends of the tubes are set with gaskets made of a fluoroelastomeric synthetic rubber, such as Viton.RTM., produced by E.I. du Pont de Nemours and Co., or of graphite, which gaskets provide a tight seal with the tubes at the orifices in the shell's end walls. A dished bottom having a pipe manifold and connecting flanges connects the lower end of the shell to circulation pipes.
Between the interior of the barriers and the exterior, a pressure differential is created which may be of the order of about ten bars. The hydrocarbon or concentrate feedstock passes into the module through said inlet piping, circulates inside the barriers, and then exits through outlet piping identical with the inlet piping. Due to the pressure differential, a sizable fraction of the hydrocarbon feedstock, known as the filtrate, traverses the barriers from the interior towards the exterior.
However, this known apparatus has a serious drawback, namely, the differential expansion which results from the difference in the coefficients of expansion between the component materials of the module and of the barriers, that is, the steel and the carbon. To absorb this expansion, the prior art makes provision for the variations in length to be absorbed by the gaskets mounted on each barrier. However, in the presence of fluids such as a suspension of solid catalyst particle fines in a liquid, the barriers cake at the level of the gaskets. Therefore, in the course of a shutdown/startup procedure of the microfiltration apparatus, and hence in the presence of considerable temperature variations, the barriers may break down, and the apparatus then no longer fulfills its function of retaining the catalyst particle fines.
This drawback is also encountered in all apparatus which generally comprise a tube bundle made of a first material that is mounted in a cylindrical body which body is made of a second material, and which materials undergo differential expansion relative to one other.